1. Field of the Invention
This invention relates to a process for the production of aldehydes by the hydroformylation of olefins and, more particularly, it is concerned with an improved process for producing aldehydes by reacting olefins, carbon monoxide and hydrogen in the presence of rhodium-containing complex compound catalysts and free ligands.
2. Description of the Prior Art
Rhodium-phosphine type or rhodium-phosphite type complexes are known as catalysts for the hydroformylation of olefins and a number of studies have been made thereon, see for example Chem. Comm., 305 (1967) Apr. 12, 1967.
The stability of a rhodium catalyst is increased by modification with phosphine, arsine or stibine, which permits practicing the oxo reaction at a rather low pressure. According to Japanese Pat. No. 903326, straight chain-rich aldehydes are prepared at a low total pressure with a low partial pressure of carbon monoxide and a high partial pressure of hydrogen in the presence of a rhodium triaryl phosphine catalyst and a triaryl phosphine ligand in a large excess to the rhodium. However, this method has the disadvantage that the hydroformylation reaction rate of an olefin is markedly decreased because of using a ligand in a large excess to rhodium, and a considerable quantity of a paraffin is formed by the hydrogenation of the olefin ["Hydrocarbon Processing" (4) 112) (1970)] due to the reaction at a low total pressure with a low partial pressure of carbon monoxide and a high partial pressure of hydrogen.
Rhodium catalysts in combination with arsines or stibines instead of phosphines have been proposed, but the studies thereof have not been made so intensively because of their lower activity compared with tertiary phosphine-rhodium catalysts.
Applicants have proposed in their U.S. Ser. No. 073,664 filed on even date herewith based on Japanese Patent Applications No. 121456/78 and 121457/78, hydroformylation of an olefin using a rhodium complex containing both a tertiary organo phosphorus ligand and tertiary organo-arsenic ligand [H Rh(CO)(ligand).sub.3 ] which is an active species for the hydroformylation in the presence of excess mixed ligands of a tertiary organo phosphorus compound and tertiary organo arsenic compound. That is to say, in the hydrogormylation of an olefin, the reaction rate is remarkably improved, the quantity of paraffin formed by the hydrogenation of the olefin is decreased and, in addition, the selectivity to normal chain aldehyde is kept similar or improved in comparison with carrying out the reaction in the presence of a tertiary organo phosphorus rhodium catalyst and excess tertiary organo phosphorus ligand. The said process is superior to the prior art from the viewpoint of efficiency of hydroformylation.
However, the present method has advantages with regard to the ease of preparing or providing the rhodium-mixed ligands catalyst of this invention.